"Because I'm telling you, when that fire's not lit, you can't train the same, you go through the motions, you can't think the same, spiritually you're not the same.

"Who's going to be able to suck it up, forget about all the medals they've won, all the belts, all the pound-for-pound accolades and the 'zeros' on their records? That's going to be the biggest factor on Saturday night."

Mayweather has complained of fragile hands in the lead-up to the fight, and Hopkins said they could also play a big part in the outcome.

"Mayweather is a slightly bigger puncher, but he has bad mitts, and when you have bad mitts, you're always thinking, 'If I punch this guy, I've got to go eight more rounds with a sore hand'.

"Ricky Hatton throws so many punches, Floyd can't afford to hurt any knuckles on his hand."

Former light-welterweight king Hatton goes into the bout, billed "Undefeated", with a 43-fight unbeaten record, while Mayweather is unbeaten in 38 professional contests.

The fight is expected to start at about 0400 GMT, although it depends on the length of the fights on the undercard.